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Monitoring Well Installation Report 16 Quik Stop Market No 121 Page 6 screen was used in these wells Extraction well RW-1 was constructed using 4-inch diameter, schedule 40 polyvinyl chloride (PVC) well casing Fifteen feet of 0 020-inch screen was used in this well The annulus between each casing and borehole was backfilled with 2112 sand to approximately 2 feet above the screen interval A bentonite clay spacer, at least 2 feet thick, was placed above the sand pack, and cement grout was pumped from above the bentonite to the surface A watertight, locking, vault box caps each well A copy of a typical well construction schematic is attached in Appendix B Well Development On January 5, 2001, monitoring wells MW-4, MW-5, MW-6, MW-7 and recovery well RW-1 were developed with a vacuum pump to (a) remove residual silts and clays left from the drilling, and (b) improve the hydraulic conductivity between the wells and the natural formation After development, the wells were allowed to recharge for several days, enabling CCI to collect a representative water sample All water collected during well development was placed in a labeled drum and left on the southeast corner of the subject property Groundwater Sampling On January 10, 2001, CCI sampled the five new wells and the three existing monitoring wells Before groundwater sampling, CCI measured the depth to groundwater using an electronic sounding tape and field-checked the wells for the presence of free-floating product by collecting a sample in a clear acrylic bailer Free-floating product was not observed Each well was purged of stagnant water prior to the collection of a sample Normal field measurements, including pH, conductivity, and water temperature, were periodically recorded during the purging process A sample was collected when these parameters stabilized to within 10% of each other Atleast three well casing volumes of groundwater were purged from each well before sampling Samples were (a) collected with a clean disposable bailer, (b) transferred to appropriate laboratory-supplied bottles, ( c) labeled, (d) logged on a chain-of-custody form, and (e) placed in a chilled ice chest for transportation to a state-certified laboratory Monitoring well purge data is summarized in data Table I Subsurface Conditions The subsurface conditions encountered in the site wells were found to be composed of alternating layers of silty sand and sand, with some silty clay and clay from the surface to approximately 25 feet in wells MW-5, MW-7 and RW-1 The material was found to be dense, with localized areas of very dense material From 32 feet to 41 feet in monitoring wells MW-4 and MW-6, a dense sand to gravelly sand was encountered In monitoring well MW-6, this granular unit changed into a silty clay to clayey silt to a depth of approximately 49 feet, with some localized "hard pan" (calcium cemented sand and/or clay) material The "hard pan" material appears to be an impediment to vertical contaminant migration From 49 feet to 60 feet, a medium dense sand